This invention relates generally to folding ladders and, more particularly, is directed to a combination ladder and height adjustable scaffold.
The use of extensible folding ladders is well known in the art, and is taught, for example in U.S. Pat. Nos. 3,692,143 to Kummerlin et al; 3,794,141 to Sturm; 4,210,224 to Kummerlin et al; 4,371,055 to Ashton; and 4,376,470 to Ashton. Such ladders generally have positioning joints at the upper ends thereof for permitting movement of the ladder between different angular positions, and releasably fixing the ladder at such selected angular positions. Such positioning joints are rigidly secured to the legs or stringers of the ladder by means of rivets or screws, and are not intended to and cannot be removed therefrom. In other words, such positioning joints form an integral part of the ladder. Such positioning joints are well known and are taught, for example, in U.S. Pat. Nos. 3,811,151 to Kuemmerlin; 4,152,810 to Martinez; 4,216,844 to Klafs; 4,377,020 to Vigo; 4,403,373 to Kummerlin; 4,407,045 to Boothe; 4,543,007 to Quiogue; 4,566,150 to Boothe; 4,645,371 to Wang; and 4,666,328 to Ryu.
In order to use such ladders in a scaffold configuration, two ladders must be provided, each for supporting one end of a board. In such case, the board merely rests on the rungs of the two ladders, and is therefore subject to slipping therefrom. Accordingly, such arrangements are not very safe. In addition, because two ladders are required, the cost is very much increased, and it is less expensive to construct a conventional scaffold without the use of ladders. However, a conventional scaffold is not very flexible. Accordingly, when it is desired to increase the height of such conventional scaffold, another layer must be added, thereby increasing the cost still further.